Increasingly, gasification is being used to convert solid waste, often referred to as waste derived fuel (WDF) into valuable forms of energy. Gasification of carbonaceous materials involves a thermal reaction between the carbonaceous material, oxygen and steam at temperatures in excess of 400° C. to generate a mixture of low weight hydrocarbons, such as methane, carbon monoxide and hydrogen known as syngas. Gasification is widely used to produce syngas for firing a boiler to generate steam, for use as a fuel in a gas engine, or for refining into chemicals, liquid fuels and hydrogen and has been identified as a key enabling technology for advanced high-efficiency, low-emission non-fossil fuel and renewable energy power generation.
The application of high temperature gasification and other medium to high combustion air input thermal processes to manage solid waste presents many difficulties, particularly because of the lack of homogeneity of the contents in terms of size and composition compared to other carbonaceous materials such as coal and biomass. The average moisture content of many types of solid waste may vary from 20-60% or higher, and the average incombustible content may vary from 5-30% or higher, with some waste charges having 100% incombustible items (e.g. glass, metals, etc.). A high incombustible content results in a high density charge with concomitant increased accumulation of incombustibles/ash content. The larger percentage of inorganic solids and ash that is not consumed by combustion processes leads to an increase in the downstream clean-up processes required to provide a syngas product stream and reduced production efficiency.
In view of the heterogeneity and composition variability of solid waste feedstock, the syngas thereby produced from gasification may also demonstrate variability in its chemical composition, calorific value, moisture content and volume. In particular, the syngas may also include pollutants whose concentrations are affected by the thermal conditions they are exposed to in downstream firing and combustion processes, such as the Destruction Rate Efficiency (DRE) of chlorinated hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), dioxins, furans, other volatile organic compounds (VOCs) and principal organic pollutants (POPs), as well as the minimization of nitrogen conversion to NOx compounds.
Traditional afterburners and secondary combustion chambers are commonly used for off-gases that are mostly or fully oxidized, however their simple one-chamber design is inefficient at handling syngas, namely a volatile gas stream containing complex CnHn hydrocarbons that unless subjected to appropriate thermal conditions of high DRE will form noxious pollutants.
Further, measurement of DRE is difficult and expensive to accomplish.
There is therefore a need for technological advancement.
Any references to background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the apparatus and process as disclosed herein.